Thin-film transistor and method of manufacturing the same

ABSTRACT

The organic thin-film transistor according to the present invention includes: a gate electrode line on a substrate in a first region: a first signal line layer in a second region; a gate insulating film covering the gate electrode line and the first signal line layer; bank layers on the gate insulating film; a second signal line layer on the bank layer over the first signal line; a drain electrode and a source electrode line which are located on the bank layers and in at least one opening between the bank layers in the first region; a semiconductor layer located at least in the opening and banked up by the bank layers, the drain electrode, and the source electrode line; and a protection film covering the semiconductor layer.

TECHNICAL FIELD

The present invention relates to thin-film transistors and methods ofmanufacturing the same, and more particularly to a thin-film transistorhaving a bank layer and a method of manufacturing the same.

BACKGROUND ART

Active-matrix display devices, such as liquid crystal display devicesand organic Electro Luminescence (EL) display devices, and the likeemploy Thin Film Transistors (TFT) in their pixel circuits.

An example of the thin-film transistors includes: a substrate; a gateelectrode on the substrate; a gate insulating film over the gateelectrode; a semiconductor layer on the gate insulating film; and asource electrode and a drain electrode which are electrically connectedto the semiconductor layer.

Semiconductor layers in thin-film transistors are often made of silicon.However, in recent years, organic materials are used for semiconductorlayers to provide organic thin-film transistors. For example, PatentLiterature 1 (PLT-1) discloses such a conventional organic thin-filmtransistor.

Here, the description is given for an example of a TFT included in apixel circuit of a display device. FIG. 12A is a top view of aconventional organic thin-film transistor 80. FIG. 12B is across-sectional view of the conventional organic thin-film transistor 80taken along line A-A′ of FIG. 11A.

As shown in FIG. 12B, the organic thin-film transistor 80 includes asubstrate 801, a gate electrode line 802 a, a first signal line layer802 b, a gate insulating film 803, a drain electrode 808, a sourceelectrode line 809, a second signal line layer 810, bank layers 807 and807, an organic semiconductor layer 811, a protection film 812, and aplanarizing layer 813. In other words, the organic thin-film transistor80 consists mainly of: a channel part 80A provided with a bottom-gateTFT; a storage capacitor part 80B; and a signal line crossing part 80C.

The channel part 80A is a bottom-gate TFT that includes the substrate801, the gate electrode line 802 a, the gate insulating film 803, thedrain electrode 808, the source electrode line 809, the organicsemiconductor layer 811 having circumference defined by the bank layers807 and 807, and the protection film 812. The storage capacitor part 80Bis a capacitor that includes the substrate 801, the gate electrode line802 a, the gate insulating film 803, and the source electrode line 809.The signal line crossing part 80C includes the first signal line layer802 b and the second signal line layer 810 which cross each other. Thereis the gate insulating film 803 between the first signal line layer 802ba and the second signal line layer 810.

CITATION LIST Patent Literature

-   [PLT-1] Japanese Unexamined Patent Application No. 10-270712

SUMMARY OF INVENTION Technical Problem

Recently, screen size increase and function improvement of displaydevices have been developed. The development requires improvement of TFTproperties and reduction of parasitic capacitance. However, under thepresent circumstances, desired TFT properties are not obtained, andtherefore quality of resulting displayed image is deteriorated.

In other words, generally, properties of the thin-film transistor in thechannel part 80A depend on an electrostatic capacitance of the gateinsulating film 803. In order to improve properties of a transistor, itis necessary to decrease a thickness of the gate insulating film 803 andto form the gate insulating film 803 using a material having a higherpermittivity than that of an oxide film. However, if the gate insulatingfilm 803 is thin, a gate leakage is increased (in other words, awithstand voltage is decreased) at an uneven part W1 of the gateelectrode line 802 a.

The same problem occurs also in the signal line crossing part 80C. Inother words, if the gate insulating film 803 is thin, a gate leakage isincreased (in other words, withstand voltage properties are decreased)at an uneven part W2 of the first signal line layer 802 b.

Furthermore, since the gate insulating film 803 is thin in the signalline crossing part 80C, a parasitic capacitance is increased at a partwhere the first signal line layer 802 b and the second signal line layer810 cross each other, thereby preventing a high-speed operation of thepixel circuit.

As described above, if the gate insulating film 803 is thin, a gateleakage is increased (in other words, withstand voltage properties aredecreased.) As result, desired properties of TFT are not obtained andtherefore quality of resulting displayed image is deteriorated.

In order to solve the above-described conventional problems, an objectof the present invention is to provide a thin-film transistor that hasimproved withstand voltage properties of a gate insulating film and areduced parasitic capacitance at a part where signal lines cross eachother, and a method of manufacturing the thin-film transistor.

Solution to Problem

In accordance with an aspect of the present invention for solving theproblems, there is provided a thin-film transistor comprising: a gateelectrode line on a substrate in a first region; a first signal linelayer on the substrate in a second region that is different from thefirst region; a gate insulating film above the substrate, the gateinsulating film covering the gate electrode line and the first signalline layer, and the gate insulating film being made of a firstdielectric film; bank layers on the gate insulating film, the banklayers each being made of a second dielectric film having a lowerpermittivity than a permittivity of the first dielectric film; a secondsignal line layer on one of the bank layers over the first signal line;a pair of a drain electrode and a source electrode line which arelocated (a) on the bank layers and (b) in at least one opening betweenthe bank layers in the second region; a semiconductor layer located atleast on the gate insulating film in one of the at least one opening andbanked up by two of the bank layers, the drain electrode, and the sourceelectrode line; and a protection film covering the semiconductor layerand banked up by the two of the bank layers, the drain electrode, andthe source electrode line.

Advantageous Effects of Invention

Thus, according to the present invention, it is possible to provide: athin-film transistor that has improved withstand voltage properties of agate insulating film and a reduced parasitic capacitance at a part wheresignal lines cross each other; and a method of manufacturing thethin-film transistor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of an organic thin-film transistor according toEmbodiment 1.

FIG. 2 is a cross-sectional view of an organic thin-film transistortaken along line A-A′ of FIG. 1, according to Embodiment 1.

FIG. 3 is a view for explaining effects of the organic thin-filmtransistor according to Embodiment 1.

FIG. 4 is a top view of an organic thin-film transistor according to avariation of Embodiment 1.

FIG. 5A is a cross-sectional view of one of steps in a method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5B is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5C is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5D is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5E is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5F is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5G is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5H is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5I is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 5J is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment1.

FIG. 6A is a cross-sectional view of one of steps in a method ofmanufacturing a conventional organic thin-film transistor.

FIG. 6B is a cross-sectional view of one of the steps in the method ofmanufacturing the conventional organic thin-film transistor.

FIG. 6C is a cross-sectional view of one of the steps in the method ofmanufacturing the conventional organic thin-film transistor.

FIG. 6D is a cross-sectional view of one of the steps in the method ofmanufacturing the conventional organic thin-film transistor.

FIG. 7 is a top view of an organic thin-film transistor according toEmbodiment 2.

FIG. 8 is a cross-sectional view of the organic thin-film transistortaken along line A-A′ of FIG. 7, according to Embodiment 2.

FIG. 9 is a view for explaining effects of the organic thin-filmtransistor according to Embodiment 2.

FIG. 10 is a top view of an organic thin-film transistor according to avariation of Embodiment 2.

FIG. 11A is a cross-sectional view of one of steps in a method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11B is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11C is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11D is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11E is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11F is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11G is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11H is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11I is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 11J is a cross-sectional view of one of the steps in the method ofmanufacturing the organic thin-film transistor according to Embodiment2.

FIG. 12A is a top view of a conventional organic thin-film transistor.

FIG. 12B is a cross-sectional view of the conventional organic thin-filmtransistor taken along line A-A′ of FIG. 12A.

DESCRIPTION OF EMBODIMENTS

In accordance with an aspect of the present invention, there is provideda thin-film transistor comprising: a gate electrode line on a substratein a first region; a first signal line layer on the substrate in asecond region that is different from the first region; a gate insulatingfilm above the substrate, the gate insulating film covering the gateelectrode line and the first signal line layer, and the gate insulatingfilm being made of a first dielectric film; bank layers on the gateinsulating film, the bank layers each being made of a second dielectricfilm having a lower permittivity than a permittivity of the firstdielectric film; a second signal line layer on one of the bank layersover the first signal line; a pair of a drain electrode and a sourceelectrode line which are located (a) on the bank layers and (b) in atleast one opening between the bank layers in the second region; asemiconductor layer located at least on the gate insulating film in oneof the at least one opening and banked up by two of the bank layers, thedrain electrode, and the source electrode line; and a protection filmcovering the semiconductor layer and banked up by the two of the banklayers, the drain electrode, and the source electrode line

It is thereby possible to provide a thin-film transistor that hasimproved withstand voltage properties of a gate insulating film and areduced parasitic capacitance at a part where signal lines cross eachother.

It is possible that the at least one opening is formed between two ofthe bank layers in a third region and a fourth region which are includedin the second region to expose a part of the gate insulating film and,the source electrode line is located (a) on the gate insulating film ina first opening in the third region among the at least one opening, (b)on a first bank layer among the bank layers between the third region andthe fourth region, and (c) on a part of the gate insulating film in asecond opening in the fourth region among the at least one opening, thepart of the gate insulating film being closer to the third region, thedrain electrode is located (a) on another part of the gate insulatingfilm in the second opening in the fourth region and (b) on a second banklayer in the fourth region among the bank layers, the another part ofthe gate insulating film and the second bank layer being farther fromthe third region, the semiconductor layer is located on the gateinsulating film in the second opening in the fourth region and banked upby at least the drain electrode and the source electrode line, and theprotection film covers the semiconductor layer and is banked up by atleast the drain electrode and the source electrode line.

It is also possible that one of the at least one opening is formedbetween two of the bank layers in the second region to expose a part ofthe gate insulating film, the source electrode line is located (a) on anend of one of the two of the bank layers and (b) on a part of the gateinsulating film in the one of the at least one opening, the end beingcloser to the one of the at least one opening, and the part of the gateinsulating film being closer to the end, the drain electrode is located(a) on another part of the gate insulating film in the one of the atleast one opening, and (b) on an other one of the two of the banklayers, the another part of the gate insulating film and the other oneof the two of the bank layers being farther from the end, thesemiconductor layer is located at least on the gate insulating film inthe one of the at least one opening and banked up by the two of the banklayers, the drain electrode, and the source electrode line, and theprotection film covers the semiconductor layer and is banked up by thetwo of the bank layers, the drain electrode, and the source electrodeline.

It is further possible that the third region is a storage capacitor partthat includes a part of the gate electrode line, a part of the gateinsulating film, and at least a part of the source electrode, and thefourth region is a channel part that includes a part of the gateelectrode line, a part of the gate insulating film, the semiconductorlayer, a part of the drain electrode, and a part of the sourceelectrode.

It is still further possible that the thin-film transistor has: astorage capacitor part that includes a part of the gate electrode line,a part of the gate insulating film, and at least a part of the sourceelectrode; and a channel part that includes a part of the gate electrodeline, a part of the gate insulating film, the semiconductor layer, apart of the drain electrode, and a part of the source electrode.

It is still further possible that the thin-film transistor furtherincludes a planarizing layer covering the second signal line layer, thesource electrode, the drain electrode, and the protection film.

It is still further possible that the drain electrode, the sourceelectrode, and the second signal line layer are made of a same material.

It is still further possible that a side surface of the at least oneopening has a forward tapered shape.

It is still further possible that the semiconductor comprises a coatingorganic semiconductor.

It is still further possible that the semiconductor comprises a coatingoxide semiconductor.

In accordance with another aspect of the present invention, there isprovided a method of manufacturing a thin-film transistor, comprising:forming (a) a gate electrode line on a substrate in a first region, and(b) a first signal line layer above the substrate in a second regionthat is different from the first region; forming a gate insulating filmabove the substrate, the gate insulating film covering the gateelectrode line and the first signal line layer, and the gate insulatingfilm being made of a first dielectric film; forming bank layers on thegate insulating film, the bank layers each being made of a seconddielectric film having a lower permittivity than a permittivity of thefirst dielectric film; forming at least one opening between two of thebank layers in the second region; a second signal line layer on one ofthe bank layers over the first signal line; forming a drain electrodeand a source electrode on the bank layers and in the at least oneopening; forming a semiconductor layer at least on the gate insulatingfilm in one of the at least one opening, the semiconductor layer beingbanked up by two of the bank layers, the drain electrode, and the sourceelectrode; and forming a protection film to cover the semiconductorlayer, the protection film being banked up by the two of the banklayers, the drain electrode, and the source electrode.

It is thereby possible to provide a method of manufacturing a thin-filmtransistor that has improved withstand voltage properties of a gateinsulating film and a reduced parasitic capacitance at a part wheresignal lines cross each other.

In accordance with still another aspect of the present invention, thereis provided a thin-film transistor, comprising: a gate electrode linelayer on a substrate; a gate insulating film on the gate electrode linelayer, the gate insulating film being made of a first dielectric film;bank layers on the gate insulating film, the bank layers each being madeof a second dielectric film having a permittivity different from apermittivity of the first dielectric film; at least one opening betweentwo of the bank layers in a region that includes a channel part and astorage capacitor part; a line layer on one of the bank layers in aregion that is different from the channel part and the storage capacitorpart; and a drain electrode and a source electrode line which arelocated on the gate insulating film in the at least one opening in thechannel part and the storage capacitor part, wherein the channel partincludes: a semiconductor layer located in the at least one opening; anda protection film covering the semiconductor layer, and thesemiconductor layer has a circumference defined by the two of the banklayers, the drain electrode, and the source electrode line in the atleast one opening in the channel part.

It is thereby possible to provide a thin-film transistor that hasimproved withstand voltage properties of a gate insulating film and areduced parasitic capacitance at a part where signal lines cross eachother.

Embodiment 1

The following describes embodiments of an organic thin-film transistorand a method of manufacturing the organic thin-film transistor accordingto the present invention. However, the present invention ischaracterized by the appended claims. Therefore, among constituentelements in the following embodiments, constituent elements that are notdescribed in claims are described as elements constituting moredesirable configurations, although such constituent elements are notnecessarily required to achieve the object of the present invention. Itshould also be noted that the figures in the drawings are schematicdiagrams and do not show the embodiments exactly.

The following describes the organic thin-film transistor 10 according toEmbodiment 1 with reference to FIGS. 1 and 2. FIG. 1 is a top view ofthe organic thin-film transistor 10 according to Embodiment 1. FIG. 2 isa cross-sectional view of the organic thin-film transistor 10 accordingto Embodiment 1 taken along line A-A′ of FIG. 1.

As shown in FIG. 2, the organic thin-film transistor 10 includes asubstrate 101, a gate electrode line 102 a, a first signal line layer102 b, a gate insulating film 103, bank layers 105, 106, and 107, adrain electrode 108, a source electrode line 109, a second signal linelayer 110, an organic semiconductor layer 111, a protection film 112,and a planarizing layer 113. In other words, the organic thin-filmtransistor 10 consists mainly of: a channel part 10A provided with abottom-gate TFT; a storage capacitor part 10B; and a signal linecrossing part 10C.

The channel part 10A is provided between the bank layer 105 and the banklayer 106. The channel part 10A has a bottom-gate TFT that includes thesubstrate 101, the gate electrode line 102 a, the gate insulating film103, the drain electrode 108, the source electrode line 109, the organicsemiconductor layer 111, and the protection film 112. The storagecapacitor part 10B is provided between the bank layer 106 and the banklayer 107. The storage capacitor part 10B has a capacitor that includesthe substrate 101, the gate electrode line 102 a, the gate insulatingfilm 103 and the source electrode line 109. The signal line crossingpart 10C includes the first signal line layer 102 b and the secondsignal line layer 110 which cross each other. There are the gateinsulating film 103 and the bank layer 107 between the first signal linelayer 102 ba and the second signal line layer 110.

The following describes each of the structural elements in more detail.

The substrate 101 is, for example, a glass substrate comprising a silicaglass or an alkali-free glass. It should be noted that the substrate 101may be a flexible substrate having a flexibility, such as a plasticfilm, or the like.

The gate electrode line 102 a is provided on a predetermined region ofthe substrate 101, and the first signal line layer 102 b is formed inthe signal line crossing part that is a region different from the abovepredetermined region on the substrate 101. In the present embodiment,the gate electrode line 102 a is patterned in a predetermined shape onthe substrate 101 in the channel part 10A and the storage capacitor part10B. Likewise, the first signal line layer 102 b is patterned in apredetermined shape on the substrate 101 in the signal line crossingpart 10C.

Each of the gate electrode line 102 a and the first signal line layer102 b has a single-layer or multi-layer structure comprising conductivematerial(s) or its(theirs) alloy(s). For example, molybdenum (Mo),aluminium (Al), copper (Cu), tungsten (W), titanium (Ti), chromium (Cr),molybdenum tungsten (MoW), and the like are used.

The gate insulating film 103 is made of a first dielectric film that isformed on the substrate 101 to cover the gate electrode line 102 a andthe first signal line layer 102 b. In the present embodiment, the gateinsulating film 103 is formed over the whole substrate 101 to cover thegate electrode line 102 a and the first signal line layer 102 b.

Here, the first dielectric film may be an inorganic insulating film thatis (a) a single-layer or multi-layer silicon nitride film, or (b) amulti-layer film including a silicon oxide film, a silicon nitride film,and/or the like. The first dielectric film may be an organic insulatingfilm comprising polyimide, polyvinyl phenol, polypropylene, or the like.

The drain electrode 108 and the source electrode line 109 in a pair areformed in respective openings of the bank layers on the gate insulatingfilm 103 (in other words, formed between the bank layer 105 and the banklayer 106, and between the bank layer 106 and the bank layer 107). Thedrain electrode 108 and the source electrode line 109 face each otherwith a predetermined interval above the gate electrode line 102 a.

In other words, the source electrode line 109 is formed in the openingbetween the bank layers in the storage capacitor part 10B, on the banklayer between the storage capacitor part 10B and the channel part 10A,and in a part of the opening which is closer to the storage capacitorpart 10B in the channel part 10A. The drain electrode 108 is provided inanother part of the opening which is at an opposite side (farther fromthe storage capacitor part 10B) in the channel part 10A, and on the banklayer 105. More specifically, the source electrode line 109 is formedon: the gate insulating film 103 in a part of the opening closer to thestorage capacitor part 10B in the channel part 10A; the bank layer 106;the gate insulating film 103 in the opening of the bank layer in thestorage capacitor part 10B (in other words, the opening between the banklayer 106 and the bank layer 107); and one edge of the bank layer 107.The drain electrode 108 is formed on: a part of the opening of the banklayer on the gate insulating film 103 (a part of the opening between thebank layer 105 and the bank layer 106); and the bank layer 105.

Furthermore, each of the drain electrode 108 and the source electrodeline 109 in a pair has a single-layer structure comprising a conductivematerial, its alloy, or the like. For example, Mo, W, Cu, Al, Au (gold),Ag (silver), MoW, MoN (molybdenum nitride), and/or the like.

In the present embodiment, the drain electrode 108 and the sourceelectrode line 109 are provided on the bank layer 105 and the bank layer106, so as to serve also as banks defining the circumference of theorganic semiconductor layer 111. More specifically, each of the drainelectrode 108 and the source electrode line 109 serves as a bankdefining the circumference of the organic semiconductor layer 111. Thedrain electrode 108 and the source electrode line 109 together with thebank layers 105 and 106 block a flow of a solvent used as the organicsemiconductor layer 111.

The bank layers (the bank layers 105, 106, and 107) are made of a seconddielectric film on the gate insulating film 103. The second dielectricfilm has a lower permittivity than that of the first dielectric film.There are openings between the bank layers in the channel part 10A andthe storage capacitor part 10B. Typically, a side surface of the openingof the bank layers in each of the channel part 10A and the storagecapacitor part 10B has a forward tapered shape.

In the present embodiment, the bank layer 105 and the bank layer 106 areprovided on the gate insulating film 103 to form an opening between themto separate the organic semiconductor layer 111 for each of pixels. Thebank layer 107 is provided on the gate insulating film 103. The banklayers 105, 106, and 107 are made of the second dielectric film having alower permittivity than that of the first dielectric film.

Here, the second dielectric film comprises a material having a lowerpermittivity than that of the first dielectric film. The seconddielectric film may be an inorganic insulating film added with F. Theinorganic insulating film is, for example, a single-layer or multi-layerfilm of silicon nitride film(s), or a multi-layer film including asilicon oxide film, a silicon nitride film, and/or the like. The seconddielectric film may be an organic insulating film added with F. Theorganic insulating film comprises polyimide, polyvinyl phenol,polypropylene, or the like.

Furthermore, the second dielectric film may comprise a sensitivematerial such as a resist. More specifically, a bank layer comprising asensitive material is formed, and the sensitive material is partiallyexposed to be developed to form an opening in the bank layer. As aresult, the bank layers 105, 106, and 107 are obtained.

The second signal line layer 110 is provided above the first signal linelayer 102 b and on the bank layer 107. The second signal line layer 110comprises the same material as that of the drain electrode 108 and thesource electrode line 109. More specifically, the second signal linelayer 110 has a single-layer structure comprising a conductive material,its alloy, or the like. For example, the second signal line layer 110comprises Mo, W, Cu, Al, Au (gold), Ag (silver), MoW, MoN (molybdenumnitride), and/or the like.

The organic semiconductor layer 111 is provided on the gate insulatingfilm 103 in the opening in the channel part 10A. Here, the organicsemiconductor layer 111 is banked up by the bank layer 105, the banklayer 106, the drain electrode 108, and the source electrode line 109.

More specifically, the organic semiconductor layer 111 is providedbetween the drain electrode 108 and the source electrode line 109 in theopening of the bank layers (in other words, the opening between the banklayer 105 and the bank layer 106) in the channel part 10A.

More specifically, the organic semiconductor layer 111 is provided atleast on the gate insulating film 103 between the drain electrode 108and the source electrode line 109. The organic semiconductor layer 111is surrounded by the side surfaces (in other words, the inner walls ofthe opening) of the drain electrode 108 and the source electrode line109 in the opening formed by the bank layer 105 and the bank layer 106.The outer circumference of the organic semiconductor layer 111 isdefined by the side surfaces (inner walls). In other words, the organicsemiconductor layer 111 is continuously provided on: the side surface(inner wall) of the drain electrode 108 in the opening of the banklayers 105 and 106; the top surface of the exposed gate insulating film103; the side surface (inner wall) of the source electrode line 109 inthe opening of the bank layers 105 and 106; and the bank layers 105 and106.

The organic semiconductor layer 111 is a coating organic semiconductorthat comprises a coating organic material. By using a printing methodsuch as an ink-jet method, the organic semiconductor layer 111 is formedby coating and crystallizing a predetermined solvent in a part betweenthe drain electrode 108 and the source electrode line 109 in the openingof the bank layers. A material of the organic semiconductor layer 111may be, for example, pentacene, phthalocyanine, or porphyrin solubleorganic material. It should be noted that the material of the organicsemiconductor layer 111 is not limited to an organic material, but maybe a coatable inorganic material. In other words, for example, theorganic semiconductor layer 111 may comprise a coating oxidesemiconductor.

The protection film 112 is provided to cover the organic semiconductorlayer 111. Here, the protection film 112 is banked up by the bank layer105, the bank layer 106, the drain electrode 108, and the sourceelectrode line 109. More specifically, the protection film 112 isprovided on the organic semiconductor layer 111 to protect the organicsemiconductor layer 111. In the present embodiment, between the drainelectrode 108 and the source electrode line 109 in the opening of thebank layers, the protection film 112 is formed to cover the organicsemiconductor layer 111. The outer circumference of the protection film112 is defined by the side surfaces (inner walls) of the drain electrode108 and the source electrode line 109 in the opening formed by the banklayer 105 and the bank layer 106.

Here, the protection film 112 desirably includes a cross-linked materialcaused by light. For the cross-linked material caused by light, lightirradiation causes molecular bonds among molecules, and the molecularstructure is densified to fortify the polymer bonds. It is therebypossible to effectively prevent water, oxygen, or impurity from enteringthe organic semiconductor layer 111. Examples of the cross-linkedmaterial caused by light are a high molecular material such as acrylicpolymer, and a low molecular material such as acrylic monomer.Furthermore, the protection film 112 desirably includes a cross-linkedmaterial caused by heat in addition to a cross-linked material caused bylight. It should be noted that the material of the protection film 112is not limited to an organic material, but may be a material generatedby adding an inorganic material such as silicon to the above-describedorganic materials. If such a material generated by adding an inorganicmaterial such as silicon to an organic material is used, it is possibleto further prevent water, oxygen, or the like from entering the organicsemiconductor layer 111, in comparison to the organic protection filmmade only of an organic material.

The planarizing layer 113 covers the second signal line layer 110, thesource electrode line 109, the drain electrode 108, and the protectionfilm 112 to smooth the organic thin-film transistor 10. In the presentembodiment, the planarizing layer 113 is provided on the drain electrode108 and the source electrode line 109 to cover fill the protection film112 to fill the opening of the bank layers. Furthermore, the planarizinglayer 113 fills an exposed part of the bank layer 107 between thestorage capacitor part 10B and the signal line crossing part 10C. Asdescribed above, the planarizing layer 113 suppresses occurrence of aleak current between layers, and smoothes the surface of the organicthin-film transistor 10. The planarizing layer 113 may comprise, forexample, an organic material such as a resist, or an inorganic materialsuch as Spin On Glass (SOG).

In other words, the provision of the planarizing layer 113 causes theprotection film 112 to prevent property deterioration of the organicsemiconductor layer 111, and causes the planarizing layer 113 to serveas an interlayer insulating layer. Therefore, the protection film 112and the planarizing layer 113 can offer the different functions. It istherefore possible to prevent property deterioration of the organicsemiconductor layer 111 and prevent a current leakage between layers. Asa result, the organic thin-film transistor 10 has a high reliability.

Thus, the organic thin-film transistor 10 has the above-describedstructure.

Next, the description is given for the effects of the organic thin-filmtransistor 10 according to Embodiment 1. FIG. 3 is a view for explainingthe effects of the organic thin-film transistor 10 according toEmbodiment 1. The identical reference numerals in FIG. 2 are assigned tothe identical elements that are not explained again below.

For the organic thin-film transistor 10, the bank layers 105, 106, and107 are formed on the gate insulating film 103. After that, the drainelectrode 108, the source electrode line 109, and the second signal linelayer 110 are formed. As a result, as shown in regions d each surroundedby a broken line in FIG. 3, the thickness of the bank layer 105 causesan unevenness of the drain electrode 108, and the thickness of the banklayer 106 causes an unevenness of the source electrode line 109.Thereby, the drain electrode 108 and the source electrode line 109 aswell as the bank layers 105 and 106 serve as banks for the organicsemiconductor layer 111.

With the above structure, the organic thin-film transistor 10 canproduce four effects described below. The four effects are as follows.

At the beginning, the first effect is explained.

Regarding the organic thin-film transistor 10, in the channel part 10A,there is the bank layer 105 between the drain electrode 108 and the gateinsulating film 103. With this structure, the bank layer 105 can cover apart of the gate insulating film 103 which is on the end of the gateelectrode line 102 a having a low withstand voltage property (lowinsulating withstand voltage). Furthermore, the bank layer 105 can keepan enough distance a between the gate electrode line 102 a and the drainelectrode 108. As a result, a leak current can be prevented. In otherwords, it is possible to improve the withstand voltage property.Likewise, in the signal line crossing part 10C, there is the bank layer107 between the second signal line layer 110 and the gate insulatingfilm 103. With this structure, the bank layer 107 can cover a part ofthe gate insulating film 103 which is on the end of the first signalline layer 102 b having a low withstand voltage property (low insulatingwithstand voltage). Furthermore, the bank layer 107 can keep an enoughdistance a between the first signal line layer 102 b and the secondsignal line layer 110. As a result, a leak current can be prevented. Inother words, it is possible to improve the withstand voltage property.

Next, the second effect is explained.

Regarding the organic thin-film transistor 10, in the signal linecrossing part 10C, there is the bank layer 107 between the second signalline layer 110 and the gate insulating film 103. With this structure, itis possible to increase a thickness of a layer between the second signalline layer 110 and the first signal line layer 102 b. As a result, aparasitic capacitance is suppressed.

Next, the third effect is explained.

Regarding the organic thin-film transistor 10, in the channel part 10A,the organic semiconductor layer 111 is provided directly on the gateinsulating film 103 without providing a bank layer between the organicsemiconductor layer 111 and the gate insulating film 103. Also in thestorage capacitor part 10B, the source electrode line 109 is provideddirectly on the gate insulating film 103 without providing a bank layerbetween the source electrode line 109 and the gate insulating film 103.As a result, the gate insulating film 103 is thin in each of the channelpart 10A and the storage capacitor part 10B. In other words, it ispossible to ensure electrostatic capacitance of the gate insulating film103 which is necessary to improve property of the organic thin-filmtransistor 10.

Finally, the fourth effect is explained.

In the organic thin-film transistor 10, the bank layers 105, 106, and107 are made of the second dielectric film having a lower permittivitythan that of the first dielectric film serving as the gate insulatingfilm 103. With this structure, in the signal line crossing part 10C, itis possible to enhance the second effect of suppressing the parasiticcapacitance. Furthermore, in the channel part 10A, it is possible toenhance the third effect of ensuring the electrostatic capacitance ofthe gate insulating film 103.

In other words, it is possible to decrease the thickness of the gateinsulating film 103 in each of the channel part 10A and the storagecapacitor part 10B, and increase a thickness of an insulating film inthe signal line crossing part 10C by providing a bank layer that is aninsulating film (for example, the second permittivity film) differentfrom the gate insulating film 103.

As a result, it is possible not only to improve the property bydecreasing the thickness of the gate insulating film 103 in the channelpart 10A, but also to increase a storage capacity in the storagecapacitor part 10B, and to reduce a signal delay (to increase anoperation speed of a pixel circuit) in the signal line crossing part 10Cby increasing the thickness of the insulating film and decreasing apermittivity.

In general, the property of the thin-film transistor in the channel part10A is defined as Ids=W/(2*L)*μ*Cox*Vds². Here, Ids represents a currentflowing from a drain to a source. μ represents a shift degree of acarrier, and Cox represents a capacity of the gate insulating film perunit area. W represents a channel width, and L represents a channellength. Vds represents a voltage between a drain electrode and a sourceelectrode. As defined above, Ids is increased in proportion to acapacity of the gate insulating film, and in proportion to W/L.Therefore, the organic thin-film transistor 10 having the abovestructure can increase the storage capacity, so that even a transistorhaving a shorter W can obtain the same Ids as that in the conventionaltechnique. In addition, the storage capacitor part 10B having a smallerarea can obtain the same the storage capacity as that in theconventional technique. This means that it is possible to provide, inthe storage capacitor part 10B, an organic thin-film transistor that hasperformance equal to the conventional performance and a smaller areathan the conventional area. In other words, the organic thin-filmtransistor can be miniaturized.

It should be noted that it has been described above that, as shown inFIG. 1, in viewing the organic semiconductor layer 111 from above, thewidth of the channel region that is a region of the organicsemiconductor layer 111 is shorter than the width of each of the drainelectrode 108 and the source electrode line 109. However, the structureis not limited to the above. For example, as shown in FIG. 4, it is alsopossible that the width of the channel region is longer than the widthof each of the drain electrode 108 and the source electrode line 109viewed from above. Here, FIG. 4 is a top view of an organic thin-filmtransistor 20 according to a variation of Embodiment 1.

Next, a method of manufacturing the organic thin-film transistor 10according to Embodiment 1 is described with reference to FIGS. 5A to 5J.FIGS. 5A to 5J are cross-sectional views for explaining respective stepsin the method of manufacturing the organic thin-film transistor 10according to Embodiment 1.

First, as shown in FIG. 5A, a material of the gate electrode line 102 aand the first signal line layer 102 b is deposited on the substrate 101to form a metal layer 102. In the present embodiment, a glass substrateis used as the substrate 101. The material of the metal layer 102 may beMo, Al, Cu, W, Ti, Cr, MoW, or the like. The metal layer 102 can beformed by spattering or vapor deposition.

Next, shown in FIG. 5B, photolithography and etching are performed topattern the metal layer 102 to form the gate electrode line 102 a andthe first signal line layer 102 b. As a result, the gate electrode line102 a and the first signal line layer 102 b have different predeterminedshapes on different regions on the substrate 101. It should be notedthat the etching for the metal layer 102 may be wet etching or dryetching.

Next, as shown in FIG. 5C, the gate insulating film 103 is formed on thesubstrate 101, covering the gate electrode line 102 a and the firstsignal line layer 102 b. The gate insulating film 103 is formed over thewhole the substrate 101 to cover the gate electrode line 102 a and thefirst signal line layer 102 b, by using plasma CVD or a coating methoddepending on the material of the gate insulating film 103. For example,the gate insulating film 103 is made of the first dielectric filmcomprising a material having a predetermined permittivity. For example,the gate insulating film 103 may be formed by plasma CVD as the firstdielectric film that is (a) a single-layer or multi-layer siliconnitride film, or (b) a multi-layer film including a silicon oxide film,a silicon nitride film, and/or the like. It should be noted that thegate insulating film 103 may be formed by a coating method as the firstdielectric film that is an organic insulating film comprising polyimide,polyvinyl phenol, polypropylene, or the like.

Next, as shown in FIG. 5D, on the gate insulating film 103, a bank layer104 made of the second dielectric film having a lower permittivity thanthat of the first dielectric film is formed. The bank layer 104 can beformed by plasma CVD or a coating method depending on the material ofthe bank layer 104. For example, the bank layer 104 is formed as thesecond dielectric film having a lower permittivity than that of thefirst dielectric film. For example, the bank layer 104 may be formed byplasma CVD as the second dielectric film that is a silicon oxide filmadded with F. It should be noted that the bank layer 104 may be formedby a coating method as the second dielectric film that is an organicinsulating film comprising polyimide, polyvinyl phenol, polypropylene,or the like added with F.

Next, as shown in FIG. 5E, the bank layer 104 is patterned to expose thegate insulating film 103, so as to form openings at predeterminedregions, which will be the channel part 10A and the storage capacitorpart 10B, over the gate electrode line 102 a. As a result, the banklayers 105, 106, and 107 having respective different predeterminedshapes are formed.

Here, the bank layers 105, 106, and 107 are formed by patterning thebank layer 104 by photolithography and etching. The predeterminedregions of the bank layer 104 are removed by etching to expose the gateinsulating film 103.1 t should be noted that the etching on the banklayer 104 may be wet etching or dry etching. It should also be notedthat, if the bank layer 104 is made of the second dielectric film thatis an organic insulating film added with F, the patterning may beperformed by exposure and development on the bank layer 104.

Next, as shown in FIG. 5F, a material of the drain electrode 108, thesource electrode line 109, and the second signal line layer 110 isdeposited on the bank layers 105, 106, and 107, and the gate insulatingfilm 103, thereby forming a metal layer 108 a. The metal layer 108 a isformed as a single-layer film comprising Mo, W, Cu, Al, Au, Ag, MoW,MoN, or the like by spattering or vapor deposition. In the presentembodiment, a single-layer film comprising MoW is formed as the metallayer 108 a.

Next, as shown in FIG. 5G, the metal layer 108 a is patterned byphotolithography and etching so as to form the drain electrode 108, thesource electrode line 109, and the second signal line layer 110 whichhave respective different predetermined shapes. The removal by theetching exposes a predetermined region, which will be the channel part10A, of the gate insulating film 103. It should be noted that theetching on the metal layer 108 a may be wet etching or dry etching.

It is thereby possible to form the second signal line layer on the banklayer 107 above the first signal line layer 102 b. It is also possibleto form the source electrode line 109 (a) in the opening between thebank layer 107 and the bank layer 106, (b) on the bank layer 106, and(c) in a part of the opening between the bank layer 106 and the banklayer 105. It is further possible to form the drain electrode 108 (a) ina part closer to the bank layer 105 in the opening between the banklayer 106 and the bank layer 105 and (b) and on the bank layer 105.

In the present embodiment, when the metal layer 108 a is patterned, thesecond signal line layer 110 of the organic thin-film transistor 10 aswell as the drain electrode 108 and the source electrode line 109 areformed at the same time by the patterning. In other words, the secondsignal line layer 110 in the signal line crossing part 10C of theorganic thin-film transistor 10 is formed together with the drainelectrode 108 and the source electrode line 109 at the same time tocomprise the same material.

For example, it is possible to form a plurality of signal linesincluding the second signal line layer 110 by patterning the metal layer108 a. It is also possible to form the drain electrode 108 as one of thesignal lines.

Next, as shown in FIG. 5H, a solution (organic semiconductor solution)including an organic semiconductor material is coated by an ink-jetmethod on the gate insulating film 103 between the drain electrode 108and the source electrode line 109 in the opening between the bank layer106 and the bank layer 105. Here, the coating solution including theorganic semiconductor material is spread on the exposed top surface ofthe gate insulating film 103, and also spread on the side surfaces andthe top surfaces of the uneven parts of the drain electrode 108 and thesource electrode line 109 in the opening between the bank layer 106 andthe bank layer 105. Furthermore, the coating region of the solutionincluding the organic semiconductor material is defined by effects ofthe unevenness of the bank layer 105 and the bank layer 106. It isthereby possible to prevent that the solution including the organicsemiconductor material from leaking to the outside of the openingbetween the bank layer 106 and the bank layer 105.

After that, a predetermined heat treatment is performed to dry thesolution including the organic semiconductor material to crystallize theorganic semiconductor material. Thereby, it is possible to form theorganic semiconductor layer 111 having outer circumference defined bythe drain electrode 108 and the source electrode line 109 in the openingbetween the bank layer 106 and the bank layer 105. Here, the drainelectrode 108 is formed on the bank layer 105 and the source electrodeline 109 is formed on the bank layer 106.

It should be noted that, in coating the organic semiconductor materialsolution by the ink-jet method, it is preferable to put drops of thesolution onto the center area of the opening between the bank layer 106and the bank layer 105. With this structure, the solution including theorganic semiconductor material is homogeneously spread in the regionsurrounded by the drain electrode 108 and the source electrode line 109in the opening between the bank layer 106 and the bank layer 105. As aresult, it is possible to form the organic semiconductor layer 111having more uniform thickness throughout. The organic semiconductormaterial may be pentacene, phthalocyanine, or porphyrin soluble organicmaterial. It should be noted that the above-described predetermined heattreatment is preferably performed at a temperature allowing the organicsemiconductor material in the solution to be crystallized without beingdecomposed by the heat, and allowing the solvent of the solution toevaporate. In the present embodiment, the heat treatment is performed atapproximately 200° C.

Next, as shown in FIG. 5I, a solution including an overcoat material,which is a material of the protection film 112, is applied by an ink-jetmethod onto the organic semiconductor layer 111 to coat the regionsurrounded by the bank layers 106 and 105, and the drain electrode 108and the source electrode line 109 in the opening between the bank layer106 and the bank layer 105. Here, the coating region of the solutionincluding the overcoat material is defined by the effects of theunevenness of each of the bank layer 105 and the bank layer 106. As aresult, it is possible to prevent the solution including the overcoatmaterial from leaking to the outside of the opening between the banklayer 106 and the bank layer 105. After coating the predetermined regionby the solution including the overcoat material, a predetermined heattreatment is performed. Thereby, the solution including the overcoatmaterial is dried to form the protection film 112 with defined outercircumference.

Here, if the overcoat material in the solution includes a cross-linkedmaterial caused by heat, the heat treatment can improve the protectionfunction of the protection film 112. Furthermore, if the overcoatmaterial includes a cross-linked material caused by light, irradiationof light such as ultra violet rays causes molecular bonds amongmolecules of the overcoat material, and the molecular structure isdensified to fortify the polymer bonds. It is thereby possible toenhance the effects of the protection film 112 to block oxygen, water,or impurity.

It should be noted that it has been described in the present embodimentthat the overcoat material is applied by the ink-jet method, but it isalso possible to apply the overcoat material to the entire surface byspin coating to produce the same effects as long as a necessarythickness is obtained on the organic semiconductor.

Next, as shown in FIG. 5J, the planarizing layer 113 is formed to coverthe second signal line layer 110, the source electrode line 109, thedrain electrode 108, and the protection film 112. The planarizing layer113 has a desired thickness to have a planar surface. It should be notedthat the planarizing layer 113 may be formed by coating a predeterminedmaterial such as SOG.

As described above, the organic thin-film transistor 10 according to thepresent embodiment can be manufactured.

Here, in order to compare with the present embodiment, a method ofmanufacturing the conventional organic thin-film transistor 80 isdescribed with reference to FIGS. 6A to 6D. FIGS. 6A to 6D arecross-sectional views for explaining steps in the method ofmanufacturing the conventional organic thin-film transistor 80.

The steps prior to FIG. 6A are the same as FIGS. 5A to 5C, so that thesteps are not described again below.

As shown in FIG. 6A, the drain electrode 808, the source electrode line809, and the second signal line layer 810 are deposited on the entiresurface of the gate insulating film 803 to form a metal layer 808 a. Themetal layer 808 a is formed by spattering or vapor deposition as asingle-layer or multi-layer film or a metal alloy film comprising Mo, W,Cu, Al, Au, Ag, MoW, MoN, and/or the like. In the present embodiment, asingle-layer film comprising MoW is formed as the metal layer 808 a.

Next, as shown in FIG. 6B, the metal layer 808 a is patterned byphotolithography and etching so as to form the drain electrode 808, thesource electrode line 809, and the second signal line layer 810 whichhave respective different predetermined shapes. The removal by theetching exposes a predetermined region, which will be the channel part80A, of the gate insulating film 803. It should be noted that theetching on the metal layer 808 a may be wet etching or dry etching.

Also in the conventional example, when the metal layer 808 a ispatterned, the second signal line layer 810 of the organic thin-filmtransistor 80 as well as the drain electrode 808 and the sourceelectrode line 809 are formed at the same time by the patterning.

Next, as shown in FIG. 6C, a material of a predetermined bank layer(bank) is coated on the entire top surface of the substrate 801 to formthe bank layer 804. Thereby, the bank layer 804 is formed on the exposedgate insulating film 803, the source electrode, and the source electrodeline 809. Here, the bank layer 804 comprises a photosensitive resin andhas a thickness of 1 μm.

Next, as shown in FIG. 6D, the bank layer 804 is pattered to re-exposethe gate insulating film 803 between the drain electrode 808 and thesource electrode line 809 to form an opening in the channel part 80A. Asa result, the bank layers 805 and 807 having respective differentpredetermined shapes are formed. The opening is formed to expose an endof the drain electrode 808 and an end of the source electrode line 809.With this structure, the bank layer 807 is formed on the exposed gateinsulating film 803 and the source electrode line 809, and the banklayer 805 is formed on the drain electrode 808.

The patterning on the bank layer 804 may be performed by exposure anddevelopment on the bank layer 804. With this structure, the bank layer807 is formed on the exposed gate insulating film 803 and the sourceelectrode line 809, and the bank layer 805 is formed on the drainelectrode 808.

In comparing the method according to the present embodiment to themethod of manufacturing the conventional organic thin-film transistor80, it is seen that the number of steps in the method is not increased.

On the other hand, between the method according to the presentembodiment and the method of manufacturing the conventional organicthin-film transistor 80, it is seen that the order of the step offorming the bank layer (the bank layers 105, 106, and 107) and the stepof forming the metal layer (the drain electrode 108, the sourceelectrode line 109, and the second signal line layer 110) is different.More specifically, for the organic thin-film transistor 10, the drainelectrode 108, the source electrode line 109, and the second signal linelayer 110 are formed after forming the bank layers 105, 106, and 107 onthe gate insulating film 103. With this, as described above, thethickness of the bank layer 105 causes the unevenness of the drainelectrode 108 and the thickness of the bank layer 106 causes theunevenness of the source electrode line 109, so that the drain electrode108 and the source electrode line 109 can serve as banks for the organicsemiconductor layer 111.

As described above, according to the present embodiment, it is possibleto provide a thin-film transistor that has improved withstand voltageproperties of a gate insulating film and a reduced parasitic capacitanceat a part where signal lines cross each other, and a method ofmanufacturing the thin-film transistor.

Embodiment 2

In Embodiment 1, the bank layer 106 is provided between the storagecapacitor part and the channel part. However, the present invention isnot limited to the structure. It is also possible not to provide anybank layer between the storage capacitor part and the channel part. Thiscase is described below as Embodiment 2.

FIG. 7 is a top view of an organic thin-film transistor 30 according toEmbodiment 2. FIG. 8 is a cross-sectional view of the organic thin-filmtransistor 30 according to Embodiment 2 taken along line A-A′ in FIG. 7.It should be noted that the same reference numerals in FIGS. 1 and 2 areassigned to the identical structural elements in FIGS. 7 and 8, so thatthe identical structural elements are not described in detail ordescribed briefly.

The organic thin-film transistor 30 according to Embodiment 2 differsform the organic thin-film transistor 10 according to Embodiment 1 instructures of a source electrode line 309, an organic semiconductorlayer 311, and a protection film 312.

More specifically, in Embodiment 2, there is no bank layer between astorage capacitor part 30B and a channel part 30A, so that the organicsemiconductor layer 311 is extended to a part in the storage capacitorpart 30B.

In other words, the organic semiconductor layer 311 is formed in aregion including the gate insulating film 103 in the opening (openingbetween the banks) so as to be located in the channel part 30A and alsothe storage capacitor part 30B. Here, the organic semiconductor layer311 is banked up by the drain electrode 108 and the source electrodeline 309.

It should be noted that the structure, such as a material, of theorganic semiconductor layer 311 except the above-described aspect is thesame as that of the organic semiconductor layer 111, so that the samestructure is not described repeatedly.

The protection film 312 is provided to cover the organic semiconductorlayer 111. Here, the protection film 312 is banked up by the drainelectrode 308 and the source electrode line 309.

The planarizing layer 313 covers the second signal line layer 110, thesource electrode line 309, the drain electrode 108, and the protectionfilm 312 to smooth the top surface of the organic thin-film transistor30.

It should be noted that the structures of the organic semiconductorlayer 311, the protection film 312, and the planarizing layer 313 exceptthe above-described aspects are the same as those of the organicsemiconductor layer 111, the protection film 112, and the planarizinglayer 113, respectively, so that the same structures are not describedrepeatedly.

Thus, the organic thin-film transistor 30 has the above-describedstructure.

Next, the description is given for the effects of the organic thin-filmtransistor 30 according to Embodiment 2. FIG. 9 is a view for explainingthe effects of the organic thin-film transistor 30 according toEmbodiment 2. The identical reference numerals in FIG. 8 are assigned tothe identical elements in FIG. 9 that are not explained again below.

For the organic thin-film transistor 30, the bank layers 105 and 107 areformed on the gate insulating film 103. After that, the drain electrode108, the source electrode line 109, and the second signal line layer 110are formed. As a result, as shown in regions d each surrounded by abroken line in FIG. 9, as effects of the unevenness of each of the banklayers 105 and 107, the drain electrode 108 and the source electrodeline 109 as well as the bank layers 105 and 107 serve as banks for theorganic semiconductor layer 111.

With the above structure, like the organic thin-film transistor 10according to Embodiment 1, the organic thin-film transistor 30 canproduce four effects described below. The four effects are as follows.

At the beginning, the first effect is explained.

Regarding the organic thin-film transistor 30, in the channel part 30A,there is the bank layer 105 between the drain electrode 108 and the gateinsulating film 103. With this structure, the bank layer 105 can cover apart of the gate insulating film 103 which is on the end of the gateelectrode line 102 a having a low withstand voltage property (lowinsulating withstand voltage). Furthermore, the bank layer 105 can keepan enough distance a between the gate electrode line 102 a and the drainelectrode 108. As a result, a leak current can be prevented. In otherwords, it is possible to improve the withstand voltage property.Likewise, in the signal line crossing part 30C, there is the bank layer107 between the second signal line layer 110 and the gate insulatingfilm 103. With this structure, the bank layer 107 can cover a part ofthe gate insulating film 103 which is on the end of the first signalline layer 102 b having a low withstand voltage property (low insulatingwithstand voltage). Furthermore, the bank layer 107 can keep an enoughdistance a between the first signal line layer 102 b and the secondsignal line layer 110. As a result, a leak current can be prevented. Inother words, it is possible to improve the withstand voltage property.

Next, the second effect is explained.

Regarding the organic thin-film transistor 30, in the signal linecrossing part 30C, there is the bank layer 107 between the second signalline layer 110 and the gate insulating film 103. With this structure, isit possible to increase a thickness of a layer between the second signalline layer 110 and the first signal line lining part 107. As a result, aparasitic capacitance is suppressed.

Next, the third effect is explained.

Regarding the organic thin-film transistor 30, in the channel part 30A,the organic semiconductor layer 311 is provided directly on the gateinsulating film 103 without providing a bank layer between the organicsemiconductor layer 311 and the gate insulating film 103. Also in thestorage capacitor part 30B, the source electrode line 309 is provideddirectly on the gate insulating film 103 without providing a bank layerbetween the source electrode line 309 and the gate insulating film 103.As a result, the gate insulating film 103 is thin in each of the channelpart 10A and the storage capacitor part 10B. In other words, it ispossible to ensure electrostatic capacitance of the gate insulating film103 which is necessary to improve property of the organic thin-filmtransistor 30.

Finally, the fourth effect is explained.

In the organic thin-film transistor 30, the bank layers 105 and 107 aremade of the second dielectric film having a lower permittivity than thatof the first dielectric film serving as the gate insulating film 103.With this structure, in the signal line crossing part 30C, it ispossible to enhance the second effect of suppressing the parasiticcapacitance. Furthermore, in the channel part 30A, it is possible toenhance the third effect of ensuring the electrostatic capacitance ofthe gate insulating film 103.

In other words, it is possible to decrease the thickness of the gateinsulating film 103 in each of the channel part 30A and the storagecapacitor part 30B, and increase a thickness of an insulating film inthe signal line crossing part 30C by providing a bank layer that is aninsulating film (for example, the second permittivity film) differentfrom the gate insulating film 103.

As a result, it is possible not only to improve the property bydecreasing the thickness of the gate insulating film 103 in the channelpart 30A, but also to increase a storage capacity in the storagecapacitor part 30B, and to reduce a signal delay (to increase anoperation speed of a pixel circuit) in the signal line crossing part 30Cby increasing the thickness of the insulating film and decreasing apermittivity.

It should be noted that it has been described above that, as shown inFIG. 7, in viewing the organic semiconductor layer 311 from above, thewidth of the channel region that is a region of the organicsemiconductor layer 311 is shorter than the width of each of the drainelectrode 108 and the source electrode line 309. However, the structureis not limited to the above. For example, as shown in FIG. 10, it isalso possible that the width of the channel region is longer than thewidth of each of the drain electrode 108 and the source electrode line309 viewed from above. Here, FIG. 10 is a top view of an organicthin-film transistor 40 according to a variation of Embodiment 2.

Next, a method of manufacturing the organic thin-film transistor 30according to Embodiment 2 is described with reference to FIGS. 11A to11J. FIGS. 11A to 113 are cross-sectional views for explainingrespective steps in the method of manufacturing the organic thin-filmtransistor 30 according to Embodiment 2. The identical referencenumerals in FIGS. 5A to 5J and 8 are assigned to the identical elementsin FIGS. 11A to 113 that are not explained again below.

The steps of FIGS. 11A to 11D are the same as FIGS. 5A to 5D, so thatthe steps are not described again below.

Next, as shown in FIG. 11E, the bank layer 104 is patterned to exposethe gate insulating film 103, so as to form openings at predeterminedregions, which will be the channel part 10A and the storage capacitorpart 10B, over the gate electrode line 102 a. As a result, the banklayers 105 and 107 having respective different predetermined shapes areformed.

Here, the bank layers 105 and 107 are formed by patterning the banklayer 104 by photolithography and etching. The predetermined region ofthe bank layer 104 is removed by etching to expose the gate insulatingfilm 103. It should be noted that the etching on the bank layer 104 maybe wet etching or dry etching. It should also be noted that, if the banklayer 104 is made of the second dielectric film comprising an organicinsulating film, the patterning may be performed by exposure anddevelopment on the bank layer 104.

If the bank layer 104 is made of the second dielectric film comprisingthe above-described material added with F, it is possible to reduce thepermittivity of the bank layer 104.

Next, as shown in FIG. 11F, a material of the drain electrode 108, thesource electrode line 309, and the second signal line layer 110 isdeposited on the bank layers 105 and 107 and the gate insulating film103, thereby forming a metal layer 308 a. The metal layer 308 a isformed by spattering or vapor deposition as a single-layer ormulti-layer film or a metal alloy film comprising Mo, W, Cu, Al, Au, Ag,MoW, MoN, and/or the like. In the present embodiment, a single-layerfilm comprising MoW is formed as the metal layer 308 a.

Next, as shown in FIG. 11G, the metal layer 308 a is patterned byphotolithography and etching so as to form the drain electrode 108, thesource electrode line 309, and the second signal line layer 110 whichhave respective different predetermined shapes. The removal by theetching exposes a predetermined region, which will be the channel part10A, of the gate insulating film 103. It should be noted that theetching on the metal layer 308 a may be wet etching or dry etching.

It is thereby possible to form the second signal line layer on the banklayer 107 over the first signal line layer 102 b. It is also possible toform the source electrode line 109 (a) on the end of the bank layer 107close to the storage capacitor part 30B and (b) in the opening betweenthe bank layer 107 and the bank layer 105 in the storage capacitor part30B. It is further possible to form the drain electrode 108 (a) in apart closer to the bank layer 105 in the opening between the bank layer107 and the bank layer 105 and (b) and on the bank layer 105.

In the present embodiment, when the metal layer 308 a is patterned, thesecond signal line layer 110 of the organic thin-film transistor 30 aswell as the drain electrode 108 and the source electrode line 309 areformed at the same time by the patterning. In other words, the secondsignal line layer 110 in the signal line crossing part 30C of theorganic thin-film transistor 30 is formed together with the drainelectrode 108 and the source electrode line 309 at the same time tocomprise the same material.

For example, it is possible to form a plurality of signal linesincluding the second signal line layer 110 by patterning the metal layer308 a. It is also possible to form the drain electrode 108 as one of thesignal lines.

Next, as shown in FIG. 11H, a solution including an organicsemiconductor material (organic semiconductor solution) is applied by anink-jet method in the opening between the bank layer 107 and the banklayer 105, in other words, on (a) the gate insulating film 103 betweenthe drain electrode 108 and the source electrode line 309 and (b) thedrain electrode in the storage capacitor part 30B. Here, the coatingsolution including the organic semiconductor material is spread on theexposed top surface of the gate insulating film 103, and also spread onthe side surfaces and the top surfaces of the uneven parts of the drainelectrode 108 and the source electrode line 309 in the opening betweenthe bank layer 107 and the bank layer 105. The coating region of thesolution including the organic semiconductor material is defined bybeing banked up by the drain electrode 108 and the source electrode line309 having the unevenness caused by the bank layer 105 and the banklayer 107, respectively, as well as the bank layer 105 and the banklayer 107. It is thereby possible to prevent that the solution includingthe organic semiconductor material from leaking to the outside of theopening between the bank layer 107 and the bank layer 105.

After that, a predetermined heat treatment is performed to dry thesolution including the organic semiconductor material to crystallize theorganic semiconductor material. Thereby, it is possible to form theorganic semiconductor layer 311 having outer circumference defined bythe bank layer 105, the bank layer 107, the drain electrode 108 and thesource electrode line 109 in the opening between the bank layer 107 andthe bank layer 305.

It should be noted that, in coating of the organic semiconductormaterial solution by the ink-jet method, it is preferable to put dropsof the solution onto the center area of the opening between the banklayer 107 and the bank layer 105. With this structure, the solutionincluding the organic semiconductor material is homogeneously spread inthe region surrounded by the drain electrode 108 and the sourceelectrode line 109 in the opening between the bank layer 107 and thebank layer 105. As a result, it is possible to form the organicsemiconductor layer 311 having more uniform thickness throughout. Theorganic semiconductor material may be pentacene, phthalocyanine, orporphyrin soluble organic material. It should be noted that theabove-described predetermined heat treatment is preferably performed ata temperature allowing the organic semiconductor material in thesolution to be crystallized without being decomposed by the heat, andallowing the solvent of the solution to evaporate. In the presentembodiment, the heat treatment is performed at approximately 200° C.

Next, as shown in FIG. 11I, a solution including an overcoat material,which is a material of the protection film 312, is applied by an ink-jetmethod onto the organic semiconductor layer 311 to coat the regionsurrounded by the bank layers 107 and 105 and the drain electrode 108and the source electrode line 309 in the opening between the bank layer107 and the bank layer 105. Here, the coating region of the solutionincluding the overcoat material is defined by being banked up by thedrain electrode 108 and the source electrode line 309 having theunevenness caused by the bank layer 105 and the bank layer 107,respectively, as well as the bank layer 105 and the bank layer 107. As aresult, it is possible to prevent the solution including the overcoatmaterial from leaking to the outside of the opening between the banklayer 105 and the bank layer 107. After coating the predetermined regionby the solution including the overcoat material, a predetermined heattreatment is performed. Thereby, the solution including the overcoatmaterial is dried to form the protection film 312 having defined outercircumference.

Here, if the overcoat material in the solution includes a cross-linkedmaterial caused by heat, the heat treatment can improve the protectionfunction of the protection film 312. Furthermore, if the overcoatmaterial includes a cross-linked material caused by light, irradiationof light such as ultra violet rays causes molecular bonds amongmolecules of the overcoat material, and the molecular structure isdensified to fortify the polymer bonds. It is thereby possible toenhance the effects of the protection film 112 to block oxygen, water,or impurity.

It should be noted that it has been described in the present embodimentthat the overcoat material is applied by the ink-jet method, but it isalso possible to apply the overcoat material to the entire surface byspin coating to produce the same effects as long as a necessarythickness is obtained on the organic semiconductor.

Next, as shown in FIG. 11J, the planarizing layer 313 is formed to coverthe second signal line layer 110, the source electrode line 309, thedrain electrode 108, and the protection film 312. The planarizing layer313 has a desired thickness to have a planar surface. It should be notedthat the planarizing layer 313 may be formed by coating with apredetermined material such as SOG.

As described above, the organic thin-film transistor 30 according to thepresent embodiment can be manufactured.

Thus, according to the present invention, it is possible to provide: athin-film transistor that has improved withstand voltage properties of agate insulating film and a reduced parasitic capacitance at a part wheresignal lines cross each other; and a method of manufacturing thethin-film transistor.

Although the organic thin-film transistor according to the presentinvention and the method of manufacturing the organic thin-filmtransistor have been described with reference to the embodiments above,the present invention is not limited to the embodiments.

The organic thin-film transistor according to the present invention istypically applicable in organic EL display devices having organic ELelements, but may be applied in other display devices havingactive-matrix substrates, such as liquid crystal display elements. Thedisplay devices having the above structure can be used as flat paneldisplay devices, and are applicable to electric devices, such astelevision sets, personal computers, and mobile telephones, which havevarious display panels.

Those skilled in the art will be readily appreciated that variousmodifications of the exemplary embodiments and combinations of thestructural elements of the different embodiments are possible withoutmaterially departing from the novel teachings and advantages of thepresent invention. Accordingly, all such modifications and combinationsare intended to be included within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The organic thin-film transistor according to the present invention canbe widely used in display devices and other various electric devices,such as television sets, personal computers, and mobile telephones.

REFERENCE SIGNS LIST

-   10, 20, 30, 40, 80 organic thin-film transistor-   10A, 30A, 80A channel part-   10B, 30B, 80B storage capacitor part-   10C, 30C, 80C signal line crossing part-   101, 801 substrate-   102 a, 802 a gate electrode line-   102 b, 802 b first signal line layer-   102, 108 a, 308 a, 808 a metal layer-   103, 803 gate insulating film-   104, 105, 106, 107, 804, 805, 807 bank layer-   108, 808 drain electrode-   109, 309, 809 source electrode line-   110, 810 second signal line layer-   111, 311, 811 organic semiconductor layer-   112, 312, 812 protection film-   113, 313, 813 planarizing layer

1. A thin-film transistor comprising: a gate electrode line on asubstrate in a first region; a first signal line layer on the substratein a second region that is different from the first region; a gateinsulating film above the substrate, the gate insulating film coveringthe gate electrode line and the first signal line layer, and the gateinsulating film being made of a first dielectric film; bank layers onthe gate insulating film, the bank layers each being made of a seconddielectric film having a lower permittivity than a permittivity of thefirst dielectric film; a second signal line layer on one of the banklayers over the first signal line layer; a pair of a drain electrode anda source electrode line which are located (a) on the bank layers whichare at least in the first region and (b) in at least one opening betweenthe bank layers in the first region; a semiconductor layer located atleast on the gate insulating film in one of the at least one opening andbanked up by two of the bank layers which are at least in the firstregion, the drain electrode, and the source electrode line; and aprotection film covering the semiconductor layer and banked up by thetwo of the bank layers, the drain electrode, and the source electrodeline.
 2. The thin-film transistor according to claim 1, wherein the atleast one opening is formed between two of the bank layers in a thirdregion and a fourth region which are included in the first region toexpose a part of the gate insulating film and, the at least one openingincludes: a first opening in the third region; and a second opening inthe fourth region, the bank layers which are at least in the firstregion includes: a first bank layer at a location including a boarderbetween the third region and the fourth region; and a second bank layerfacing the first bank layer via the semiconductor layer, the sourceelectrode line is located (a) on the gate insulating film in the firstopening (b) on the first bank layer, and (c) on a part of the gateinsulating film in the second opening, the part of the gate insulatingfilm being closer to the third region, the drain electrode is located(a) on another part of the gate insulating film in the second opening,and (b) on the second bank layer, the another part of the gateinsulating film being closer to the second bank layer, the semiconductorlayer is located on the gate insulating film in the second opening andbanked up by at least the drain electrode and the source electrode line,and the protection film covers the semiconductor layer and is banked upby at least the drain electrode and the source electrode line.
 3. Thethin-film transistor according to claim 1, wherein one of the at leastone opening is formed between two bank layers of the bank layers whichare at least in the first region to expose a part of the gate insulatingfilm, the source electrode line is located at least in a region of apart of the gate insulating film in the one of the at least one opening,the region being adjacent to a bank layer closer to the second regionamong the two bank layers, the drain electrode is located at least (a)on an other bank layer of the two bank layers which are at least in thefirst region and (b) on another part of the gate insulating film in theone of the at least one opening, the other bank layer facing the banklayer via the one of the at least one opening and being farther from thesecond region, and the another part of the gate insulating film beingadjacent to the other bank layer, the semiconductor layer is located atleast on the gate insulating film in the one of the at least one openingand banked up by the two bank layers, the drain electrode, and thesource electrode line, and the protection film covers the semiconductorlayer and is banked up by the two bank layers, the drain electrode, andthe source electrode line.
 4. The thin-film transistor according toclaim 2, wherein the third region is a storage capacitor part thatincludes a part of the gate electrode line, a part of the gateinsulating film, and at least a part of the source electrode line, andthe fourth region is a channel part that includes a part of the gateelectrode line, a part of the gate insulating film, the semiconductorlayer, a part of the drain electrode, and a part of the source electrodeline.
 5. The thin-film transistor according to claim 1, wherein thethin-film transistor has: a storage capacitor part that includes a partof the gate electrode line, a part of the gate insulating film, and atleast a part of the source electrode line; and a channel part thatincludes a part of the gate electrode line, a part of the gateinsulating film, the semiconductor layer, a part of the drain electrode,and a part of the source electrode line.
 6. The thin-film transistoraccording to claim 1 further comprising a planarizing layer covering thesecond signal line layer, the source electrode line, the drainelectrode, and the protection film.
 7. The thin-film transistoraccording to claim 1, wherein the drain electrode, the source electrode,and the second signal line layer are made of a same material.
 8. Thethin-film transistor according to claim 1, wherein a side surface of theat least one opening has a forward tapered shape.
 9. The thin-filmtransistor according to claim 1, wherein the semiconductor layercomprises a coating organic semiconductor.
 10. The thin-film transistoraccording to claim 1, wherein the semiconductor layer comprises acoating oxide semiconductor.
 11. A method of manufacturing a thin-filmtransistor, comprising: forming (a) a gate electrode line on a substratein a first region, and (b) a first signal line layer above the substratein a second region that is different from the first region; forming agate insulating film above the substrate, the gate insulating filmcovering the gate electrode line and the first signal line layer, andthe gate insulating film being made of a first dielectric film; formingbank layers on the gate insulating film, the bank layers each being madeof a second dielectric film having a lower permittivity than apermittivity of the first dielectric film; forming at least one openingbetween two of the bank layers which are at least in the first region; asecond signal line layer on one of the bank layers over the first signalline layer; forming a drain electrode and a source electrode line on thebank layers which are at least in the first region and in the at leastone opening; forming a semiconductor layer at least on the gateinsulating film in one of the at least one opening, the semiconductorlayer being banked up by two of the bank layers which are at least inthe first region, the drain electrode, and the source electrode line;and forming a protection film to cover the semiconductor layer, theprotection film being banked up by the two of the bank layers, the drainelectrode, and the source electrode line.
 12. A thin-film transistor,comprising: a gate electrode line on a substrate; a gate insulating filmon the gate electrode line, the gate insulating film being made of afirst dielectric film; bank layers on the gate insulating film, the banklayers each being made of a second dielectric film having a permittivitydifferent from a permittivity of the first dielectric film; at least oneopening between two of the bank layers which are at least in a regionthat includes a channel part and a storage capacitor part; a line layeron one of the bank layers in a region that is different from the channelpart and the storage capacitor part; and a drain electrode and a sourceelectrode line which are located on the gate insulating film in the atleast one opening in the channel part and the storage capacitor part,wherein the channel part includes: a semiconductor layer located in theat least one opening; and a protection film covering the semiconductorlayer, and the semiconductor layer has a circumference defined by thetwo of the bank layers, the drain electrode, and the source electrodeline in the at least one opening in the channel part.